Sharif University of Technology, Kish Islan Campus 1 Internet networking basics These power point slides have been adapted from slides prepared by authors of this book: Computer Networking: A Top Down Approach Featuring the Internet , 3rd edition. Jim Kurose, Keith Ross Addison-Wesley, July 2004. Behzad Akbari
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Sharif University of Technology, Kish Islan Campus
1
Internet networking basics
These power point slides have been adapted from slides prepared by authors of this book:Computer Networking: A Top Down Approach Featuring the Internet, 3rd edition. Jim Kurose, Keith Ross Addison-Wesley, July 2004.
Behzad Akbari
Sharif University of Technology, Kish Islan Campus
2
Introduction
Our goal: get “feel” and
terminology more depth, detail later
in course approach:
use Internet as example
Overview: what’s the Internet what’s a protocol? network edge network core access net, physical media Internet/ISP structure Internet layering model
Sharif University of Technology, Kish Islan Campus
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Outline
What is the Internet?
Network edge
Network core
Network access and physical media
Internet structure and ISPs
Internet Protocol layers, service models
Sharif University of Technology, Kish Islan Campus
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What’s the Internet: “nuts and bolts” view
millions of connected computing devices: hosts = end systems
pieces allocated to calls resource piece idle if not
used by owning call (no sharing)
dividing link bandwidth into “pieces” frequency division time division
Sharif University of Technology, Kish Islan Campus
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Circuit Switching: FDM and TDMFDM
frequency
time
TDM
frequency
time
4 users
Example:
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Numerical example
How long does it take to send a file of 640,000 bits from host A to host B over a circuit-switched network? All links are 1.536 Mbps Each link uses TDM with 24 slots 500 msec to establish end-to-end circuit
Work it out!
Sharif University of Technology, Kish Islan Campus
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Network Core: Packet Switching
each end-end data stream divided into packets
user A, B packets share network resources
each packet uses full link bandwidth
resources used as needed
resource contention: aggregate resource
demand can exceed amount available
congestion: packets queue, wait for link use
store and forward: packets move one hop at a time Node receives complete
packet before forwardingBandwidth division into “pieces”
Dedicated allocation
Resource reservation
Sharif University of Technology, Kish Islan Campus
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Packet Switching: Statistical Multiplexing
Sequence of A & B packets does not have fixed pattern statistical multiplexing.
In TDM each host gets same slot in revolving TDM frame.
A
B
C10 Mb/sEthernet
1.5 Mb/s
D E
statistical multiplexing
queue of packetswaiting for output
link
Sharif University of Technology, Kish Islan Campus
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Packet switching versus circuit switching
1 Mb/s link each user:
100 kb/s when “active” active 10% of time
circuit-switching: 10 users
packet switching: with 35 users, probability
> 10 active less than .0004
Packet switching allows more users to use network!
N users
1 Mbps link
Sharif University of Technology, Kish Islan Campus
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Packet switching versus circuit switching Great for bursty data
resource sharing simpler, no call setup
Excessive congestion: packet delay and loss protocols needed for reliable data transfer,
congestion control Q: How to provide circuit-like behavior?
bandwidth guarantees needed for audio/video apps still an unsolved problem (chapter 6)
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Packet-switching: store-and-forward
Takes L/R seconds to transmit (push out) packet of L bits on to link or R bps
Entire packet must arrive at router before it can be transmitted on next link: store and forward
delay = 3L/R
Example: L = 7.5 Mbits R = 1.5 Mbps delay = 15 sec
R R RL
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Packet-switched networks: forwarding Goal: move packets through routers from source to
destination we’ll study several path selection (i.e. routing) algorithms
(chapter 4) datagram network:
destination address in packet determines next hop routes may change during session analogy: driving, asking directions
virtual circuit network: each packet carries tag (virtual circuit ID), tag determines next
hop fixed path determined at call setup time, remains fixed thru call routers maintain per-call state
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Network Taxonomy
Telecommunicationnetworks
Circuit-switchednetworks
FDM TDM
Packet-switchednetworks
Networkswith VCs
DatagramNetworks
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Outline
What is the Internet?
Network edge
Network core
Network access and physical media
Internet structure and ISPs
Internet Protocol layers, service models
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Access networks and physical media
Q: How to connect end systems to edge router?
residential access nets institutional access
networks (school, company) mobile access networks
Keep in mind: bandwidth (bits per second)
of access network? shared or dedicated?
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Residential access: point to point access Dialup via modem
up to 56Kbps direct access to router (often less)
Can’t surf and phone at same time: can’t be “always on”
ADSL: asymmetric digital subscriber line up to 1 Mbps upstream (today typically < 256 kbps) up to 8 Mbps downstream (today typically < 1 Mbps) FDM: 50 kHz - 1 MHz for downstream 4 kHz - 50 kHz for upstream
0 kHz - 4 kHz for ordinary telephone
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Residential access: cable modems
HFC: hybrid fiber coax asymmetric: up to 30Mbps downstream, 2 Mbps
upstream network of cable and fiber attaches homes to ISP router
homes share access to router deployment: available via cable TV companies
Sharif University of Technology, Kish Islan Campus